Motor tuning arrangement



DecQZB, 1941. w, VAN ROBERTS 2,267,135

MOTOR TUNING ARRANGEMENT Filed June 10, 1959 INVENTOR W, WALTER VAN 5.ROBERTS ATTORN EY Patented Dec. 23, 1941 MO'lOlRl TUNING ARRANGEMENTWalter van B. Roberts, Princeton, N. 1., minor to Radio Corporation ofAmerica, a corporation of Delaware Application June 10, 1939, Serial No.278,490

Claims.

The present invention relates broadly to motor circuits and moreparticularly to improvements in motor circuits employed as the drivingmeans for adjustable elements of radio signalling apparatus.

In motor tuning devices of the type employing a disk and a cooperatingsliding contact which devices are intended to be stopped by the slidingcontact reaching an insulated portion or segment of the disk, thedliiiculty has arisen that if the insulating segment is madesuiflciently narrow to insure breaking the motor circuit at a precisesingle point, then the inertia of the driving mechanism is liable tocarry the sliding contact entirely across the insulated segment. Whenthe disk is of the type which is so arranged that a reversible motortends to turn the disk in such a direction as to bring the segment andthe sliding contact together with the least travel, the result is thatafter passing the segment the motor reverses and comes back to it. Itmay even over-shoot the segment more than once and this behavior is whatis termed hunting.

When the motor control circuit is of the type employing a single diskwhich is arranged so that the motor drives the disk in one directiononly, so that the desired position is always approached from one side,the insulated segment must be made very narrow in order that closelyadjacent stations may be tuned to in instances where the motor controlcircuit is utilized to operate a variable tuning instrumentality. Insuch cases the result of the sliding contact overrunning the insulatingsegment is that after passing the insulated segment, the motor is againenergized thus causing a complete revolution of the disk. This may go onand on and thus prevent proper adjustment of the device. It is, ofcourse, possible to eliminate this eifect in both the instances abovediscussed by running the motor extremely slowly but this involves anundesirable delay in the time-of tuning. v

In accordance with a feature of the present invention, rapid tuning isefiected by running the motor at high speed until the contact is nearthe insulating segment and then automatically reducing the speed of themotor so that upon reaching the segment there is not sufllcient momentumin the motor to carry the contact beyond the segment. In accordance witha further feature of the present invention, precise setting is insuredmechanically by arranging the sliding contact so as to drop into asharply defined notch in-the insulating segment, the size 01' this notchand the contact pressure being so related as to produce a torque on thedisk sumcient to turn the tuning assembly in the absence of mechanicalconnection to the motor. It will be appreciated that when the contact issuddenly stopped by hitting the bottom of the notch, great force wouldbe developed by the motor even though its momentum was very small it themechanical connection between the motor and the disk were rigid. Inaccordance with another ieature of the present invention this difllcultyis avoided by drivingthe disk through a mechanical coupling having apredetermined amount of lost motion.

The various novel features of the invention will be better understood byreference to the accompanying drawing wherein,

Fig. 1 illustrates schematically one form which the invention may takein a motor control circuit employing a plurality of adjustable contactelements cooperating with a single disk and wherein the disk is alwaysrotated in one direction;

Fig. 2 illustrates in a schematic way the invention applied to a motorcircuit which employs a so-called "split commutator and a reversiblemotor; and,

Fig. 3 is a schematic showing of a form of the invention in a motorcontrol circuit wherein an individual settable commutator ring isprovided for each station to be tuned to.

Referring to Fig. 1 of the drawing, l indicates a grounded metal diskrigidly attached to a shaft 2. The shaft 2 may be connected to anyvariable element that it is desired to operate such as a tuningcondenser of a radio receiving system. A driving motor III which, aswill be pointed out below, is coupled to the disk I through a meansproviding a small amount of lost motion, has one terminal connected toground and the other to one side'oi a suitable source of voltage l2.Cooperating with the disk I are four adjustable sliding contacts 80, 9b,9c and 9d. Each of the sliding contacts is connected to the otherterminal of said source l2 through separate circuits which includerespectively switches or push buttons Ila, llb, Ho and lid. It is to beunderstood that the motor rotates the disk I in one direction only asindicated by the arrow. The disk I is provided with two inserts orsegments 5 and 5a. Segment 5 is made of insulation material and segment5a is made of a conducting material which has an appreciably higherelectrical resistance value than the mtaerial of which the disk I ismade. Segment 5 is provided with a notch into which the ends of any oneof the sliding contacts Sit-9d fits,

Let us now suppose that one of the switches l|a-l Id is closed toinstitute the operation of the motor I0. A circuit is completed fromground through motor III, source or voltage II, the particular switch orpush button lIa-lld which has been closed, the sliding contact Sic-9d,corresponding to the push button which has been closed, 'disk I, back toground, thus completing the circuit and operating the motor so as toturn the disk in the direction indicated continuation of the circledefined by disk I, is

chosen suflicient for the motor to slow down to a speed such that uponbreaking its circuit itwill not coast as far as corresponds to theamount of lost motion provided by the coupling between the motor and thedisk. When the sliding contact reaches the portion of segment 5 wherethe profile is cut away to form a notch,

the pressure on the sliding contact causes the disk to jump ahead andtake up the, lost motion.

The angular distance between the bottom of. thenotch and the junction ofsegments 5 and 5a is preferably chosen less than the angular lost motionso that even were the motor to stop just as the sliding contact passesthe junction between segments 5 and 5a the lost motionwould have alreadypermitted the sliding contact device to reach the bottom of the notch.On the other hand the motor may coast a" distance corresponding to thelost motion beyond its position at the time the slider reaches thebottom of the notch without taking up the lostmotion and affecting theproper seating of the sliding contact in the notch.

In the arrangement shown in Fig. 1 the operator has closed the switch orpush button Ho and the motor III has rotated the disk I in the directionof the arrow to the point where the sliding contact 90 is in contactwith the high resistance segment So so that in effect resistance hasbeen inserted in the motor circuit thus slowing down the motor. Thus thedisk is driven at a reduced speed until the sliding contact 9c hits theinsulating segment 5 at which time the motor circuit will be broken eventhough the switch or push button I I is maintained closed. Thepressureof the sliding contact Be on the disk I will force the disk torotate by taking up the lost motion until the sliding contact 90 isflrmly'seated' within the notch formed within the insulating segment}.The switches Ila-lld are of the type that spring open when the operatorreleases'then'i. It is to,be understood, of course,

' that the motor operates the disk I at a high speed upon closure ofanyof switches Ila-I Id 'when-the -corresponding sliding contact 90-911located anywhere except in contact with :either segment or segment So sothat if we that switch Ila is closed the motor I0 will operate the diskI at high speed until the segment 5a reaches the sliding contact So atwhich time the added resistance which the mo-. torcurrenl; encountersthrough segment 5a slows down flie motor.

I It is not necessary that segment 51: be composed a: high resistivitymaterial as it may be a i segment insulated from the body oi the diskexcept by way of a lumped resistance path. Such an arrangement has beenshown in Fig. 2 of the drawingwherein the disk I is this time composedor suitable insulation material and the commutator is made up or twosections In and lb fixed to the outer portion of the disk I. The shaft 2in this case is driven by reversible motor Ilia through a couplinghaving a predetermined amount of lost motion. The segments la and 6bseparated by the insulating segment 5 are connected respectively tosections In. and lb oi the split commutator through lumped resistors 8aand 817 respectively. ments 6a and to may be made out of exactly thesame material as the material of which sections Ia and lb'of thecommutator are made.

, The remaining portion of the circult'shown in Fig. 2- is thesame asthat shown in Fig. 1 except that due to the fact that a reversible motoris employed two sources ofthe voltage Ila and I2!) are provided. Thearrangement shown in Fig. 2

. operates as follows:

Suppose that switch or push button lie is depressed or closed as shownthenthe motor circuit is completed as follows: From ground throughswitch I Ic,sliding contact 9c,segment8a,

I resistor 8a, section Ia of the commutator, battery I'ia, motor Ilia,back to ground. The motor Illa which is provided with a suitable field10b here 3, -shown' generally as a magnet with south and 1 north poles,being'energized-by the battery Ila will rotate the shaft 2counter-clockwise at a reduced-s'peed (due to resistor 8a being in themotor circuit) until the sliding brush or contact 9c reaches theinsulating segment '5 at which time the motor circuit is broken and thespring force of the sliding. contact 90 rotates the disk 1 until thecontact is seated in the notch as previously described in connectionwith Fig, 1. If the switch Ila had been operated, the motor circuitwould be completed through sliding contact 9a,

, section .Ib of the commutator and battery Ill),

insertion of resistor 8b in the motor circuit.

thus causing the motor Illa torotate the disk] clockwise ata high speeduntil segment 06 reachedsliding contact So at which time the speed ofthe motor would be reduced due to the Then upon the insulating segment 5reaching the brush 9a the motor circuit would be broken and the springforce of sliding contact would" tak up the lostinotion between themotorand the disk and accurately seat itself in the notch. It is to beunderstood that the amount'or insulation at the junction of segment toand "segment Ia, and at the junction of segment") and section Ib issuificiently narrow so that the mo! mentum of the device prevents thesystem from stopping when the particular brush all-9b corresponding tothe push button I-la-lld depressed; reaches the insulated junction area.

Reference will now be had to Fig. 3 which shows in detail thearrangement for providingcoupling with lost motion between the motor andthe disks. For this purpose the end of the shaft 2' which is near themotor is provided with a square cross section which fits into squarehole I! formed in the gear I4. The gear I4 is in meshwith pinion I5attached to the shaft of motor ll. The

shaft 3 is sufiiciently smaller than the hole I! in gear I4 to provide apredetermined small amount a suitable resilientmaterial in order 'toreduce In this way the segmechanical shock when the lost motion is takenup. It is to be understood, of course, that lost motion may beintroduced in a variety of other ways with equally good results. Themechanism shown in Fig. 3 utilizes a separate commutator for eachstation to be tuned to by the condenser II the rotor of which isattached to the shaft 2. Thus, commutator It may be adjusted on theshaft 2 by a suitable set screw or other arrangement not shown so thatthe position of the insulation segment 5 corresponds to the position ofthe condenser at which a desired station is tuned to. It is to beunderstood that the segments Ii and 5a of commutators I and i1correspond to the two segments bearing the same numerals of thecommutator I shown in Fig. 1. For tuning to another station by means ofpush buttons or switch Ila another disk i1 is provided which is alsoadjustable on the shaft 2 to any desired position. The brushes lid andlib are spring pressed on the commutators in any suitable fashion.

One particular construction that is found to be suitable is to constructthe brushes lid and lib of resilient material and mount them on suitableblocks I91: and I9!) respectively in such a way that the correct amountof pressure is exerted upon the periphery of the respective disks orcommutators I1 and I6 so that the force exerted by the brushes issufilcient to seat the V- shaped ends of the brushes accurately withinthe notches provided in the insulation segments 5 as previouslydescribed.

In Fig. 3 the metal disks l6 and I! are grounded through the shaft 2 anda suitable ring and brush arrangement 20. While only two disks have beenshown it is to be understood that any number thereof may be utilizeddepending upon the number of stations desired to be tuned toautomatically.

The description of the illustrative embodiments is not intended asdefining the limits of the invention, and it will be understood that theinvention may be variously modified and embodied within the scope of theappended claims.

I claim:

1. In a motor control system an adjustable shaft, a contact member ofconducting material mounted on said shaft, said contact member beingprovided with a section of insulation material formed along a portion ofits surface, a notch formed in said-section, a motor for driving saidadjustable shaft, a motor circuit completed through said contact member,said motor being coupled to said shaft through means having appreciablelost motion whereby said shaft may be adjusted within the limits of saidlost motion without rotating said motor, an auxiliary driving means forsaid shaft comprising a spring pressed device positioned so as to slidealong the surface of the contact member and arranged so as to be forced,through the action of the pressure exerted by the spring, into thecenter of the notch formed in the insulation section when the shaft isadjusted to a position element, said contact element being arranged toslide over a predetermined portion of the surface area of the conductingring assembly, a pair of adjacent inserts formed in said ring inthe pathof said contact element, one of said inserts being composed ofinsulation material for breaking themotor control circuit when thecontact element is over said insulation insert, the other of saidinserts being composed of a conducting material which has a higherelectrical resistance than I the material of which the conducting ringis made for inserting a resistance in the motor control circuitsufllcient to operate the motor at a reduced speed when the contactelement is over said last named insert.

3. The invention defined by the next preceding claim characterized bythat the insert of insulation material is provided with a notch intowhich the brush contact element is forced by means of a spring when thering assembly is adjusted to a position where the brush contact elementis just entering the notch.

4. In a control system for signalling apparatus having an adjustablemember, a motor mechanically connected to said member for driving themember to be adjusted rapidly toward a predetermined position, means forslowing down the motor prior to reaching said position, means forentirely discontinuing the driving torque of said motor subsequently tosaid slowing down but prior to reaching said position, lost motion inthe mechanical connection between said motor and said member andmechanical means for bringing said member accurately to saidpredetermined position from theposition occupied at the cessation ofsaid torque.

5. In a motor control device, a member to be adjusted;a motor coupled tosaid member through a device having a predetermined amount of lostmotion, a motor circuit including means for controlling the operation ofthe motor so as to adjust said member rapidly toward a predeterminedposition and means for slowing down the motor prior to said memberreaching said position, means for de-energizing the motor subsequentlyto said slowing down but prior to reaching said position and mechanicalmeans acting independently of the motor for bringing said memberaccurately to said position through take-up of said lost motion.

6. In a motor control circuit for a motor which is adapted to adjust anadjustable member to any one of several different predeterminedpositions through selective operation of anyone of a plurality ofselectively operable means, means for coupling the adjustable member tothe motor through a device having a predetermined amount of lost motion,means controlling the operation of the motor so as to adjust said memberrapidly toward a selected one of said predetermined positions when theamount of adjustment of said adjustable member necessary to reach theselected one of said positions is greater than a predetermined amount,means for operating the motor at a reduced speed when the remainingamount of adjustment necessary to reach the selected position is in arange bounded by said predetermined amount and a position just short ofthe desired selected position, means for de-energizing the motor whensaid position which is just short of the selected position is reachedand means acting independently of the motor for bringing said memberaccurately to said desired position through take-up of the lost motion.

7. In an arrangement for adjusting a variable device to any one of a pluality of desired positions, a movable member movable with said variabledevice, an electric motor coupled to said movable member through meansprovided with a predetermined amount of lost motion, said movable memberbeing provided with a contact surface composed of conducting material, abrush contact device positioned with respect to said movable member soas to be in sliding contact with said contact surface, said contactsurface having provided thereon a segment of insulation material havinga V-shaped notch formed therein, said brush contact device beingproportioned in respect to said notch so that the contact device canslip into and be held substantially snugly within the notch when themovable member is in such a position that the notch portion of thecontact surface is under the brush contact device, said contact surfaceand cooperating brush constituting a switching means which iseffectively closed in all positions of the movable member when thecontact brush device is in sliding contact with the portion of thecontact surface composed of conducting material and effectively open inall positions of the movable member where the brush device is entirelyin sliding contact with the segment of insulation material, a pair ofterminals adapted to be connected to a source of motor operatingvoltage, circuit means including said switching device for connectingthe motor across said terminals, means for mechanically pressing saidcontact device against said contact surface with-suflicient force toaccurately center the contact device within said notch by movement ofsaid movable member through take-up of said lost motion andindependently of the driving motor, when the movable member is adjustedto a position at which the contact device is just entering the notch.

8. In an arrangement of the type described in claim 7 wherein a sectionof said contact surface composed of conducting material and adjacent thesegment of insulation material is composed of a material which whileconducting has substantially greater electrical resistance than saidfirst named conducting material whereby a resistance is in effectinserted in said circuit means in all positions of the movable memberwhere the contact brush device is in sliding contact with said highresistance portion of the contact surface.

9. In an arrangement 'of the type described in claim 7 wherein a sectionof said contact surface composed of conducting material adjacent thesegment of insulation materialis insulated from the contact surfacecomposed of conducting material except for a connection thereto througha resistor element whereby a resistance is effectively inserted in saidcircuit means in all positions of the movable member where the contactbrush device is in sliding contact with said section of the contactsurface adjacent the segment of insulation material.

10. In a motor control system, an adjustable member, a motor foractuating said adjustable member to diflerent predetermined positions, asource of voltage for said motor, position determiningmeans associatedwith said motor and including a conducting ring member coupled to saidadjustable member and movable therewith and a brush contact deviceslidable along a portion of the surface of the conducting ring, anelectrical circuit including said source, the motor and a slidingconnection between the conducting ring and the motor, a section ofinsulation material formed on a. portion of the surface of theconducting ring over which the brush slides for interrupting the motorcircuit when said brush contact device is over said insulation materialportion of the'conducting ring, another portion of the conducting ringalong the surface over which the brush contact slides and locatedadjacent the iusulation section being formed of a conducting materialwhich has sufflciently higher electrical resistance than the main partof the conducting ring to cause appreciable reduction in speed of themotor when the brush contact device is over said last named portion ofthe conductingring.v

WALTER van B. ROBERTS.

